BigPatents India

A process for purifying p-phenylenediamine color developers in their free-base form. The process includes subjecting a solution containing p-phenylenediamine-type free base color developer to short path distillation which includes at least one of falling film evaporator, thin film evaporator, wiped film evaporator, or short-path evaporator. Another aspect is a method for preparing an acid salt from a p-phenylenediamine free base color developer. The method includes the steps of: a) dissolving a purified p-phenylenediamine free base derived from the short path distillation process in an organic solvent; b) contacting the dissolved free base distillate with an appropriate mineral acid; and c) crystallizing the color developer in the acid salt form.